When a shielded circular coil with n turns and a radius of a meters is placed near the surface of a semi-infinite medium having a conductivity of sigma mhos per meter, the incremental resistance in ohms is given by delta R equals 19.92 FM to the 2nd power a to the 3rd power n to the 2nd power gamma sigma (1) where FM is the frequency in megahertz and gamma is a known function of the ratio of the distance the coil is from the surface to the radius of the coil. Since delta R can be calculated from measurements made with an RF impedence meter, (1) offers a relatively straightforward method for the in vivo evaluation of the conductivity of individual organs at the time of surgery without invading the organ. A variety of experimental units having coil radii in the range of 0.95 cm through 2.45 cm have been used in making measurements at 20, 10, 5, and 2.5 megahertz. Good agreement with results obtained with more conventional techniques has been achieved in measurements made on the surface of extended agar-NaCl regions having conductivities in the range of 0.17 through 1.07 mhos per meter. Further probe development and in vivo measurements in dogs to find sigma as a function of frequency for different organs and types of tissue are planned.